The Research on Magnetic and Transport Properties for Heusler Alloy Mn2PtSn and Hexagonal MnNiGa Alloy Thin Films

Author:Li Yue Qing

Supervisor:liu zhong yuan wang wen hong


Degree Year:2017





Spintronics is an emerging discipline,and its vigorous development greatly promotes the progress of modern information technology.In traditional semiconductor devices,people only use its charge properties.Not only the charge properties but also its spin is contained in spintronics,which greatly enriches the research content of traditional electronics,and provides a train of thought for the development of a large number of new devices.The research of functional magnetic films is an important branch of spintronics.Recently,the discovery of the skyrmion topological magnetic structure in magnetic materials sets off a boom in magnetism research.The advantages of skyrmion,such as small size,high stability and mobility,make it hold great promise to build future high density,high speed and low energy consumption magnetic information storage devices.Due to its special spin magentic structure,skyrmion will lead to rich and innovative transport physical phenomena in the real space,such as the topological Hall effect.Researching and understanding the magnetic and spin-related transport properties will provide important theoretical and guiding significance for the realization of the next generation of new spin topology memory devices.In this paper,the Heusler alloy Mn2PtSn and hexagonal MnNiGa alloy were selected as the main research objects.The magnetron sputtering technique was used to successfully fabricate the above two polycrystalline films.The crystal structure,magnetic properties and spin related transport properties of the two thin films were studied in detail,and the magnetic origin was analyzed by the first principles calculations.The magnetic and transport properties of the Heusler alloy Mn2PtSn film were investigated.The magnetron multi-target co-sputtering technique was used to prepare the Mn2PtSn thin film.The magnetic and transport properties of the Mn2PtSn film were measured.The anomalies in magnetic properties,the resistance curve,the magnetoresistance curve and the abnormal Hall resistance were observed in Mn2PtSn film,which was different from the traditional behavior of ferromagnetic metals.A quite large topological Hall effect(THE)was observed in a wide temperature range of 10K-300K for Mn2PtSn thin film,and the value of THE reached a maximum of 0.57μΩcm around 150K,which was the largest value among the THE-hosting metallic materials so far.It was concluded that the large topological Hall resistance of Mn2PtSn was caused by the skyrmion topological spin structure.The magnetic and transport properties of hexagonal MnNiGa films were investigated.The hexagonal MnNiGa films with different deposition temperatures and different deposition thicknesses were prepared by magnetron sputtering technique,and the structure,magnetic properties and transport properties were measured.XRD results showed that MnNiGa film samples were impure and contained non-magnetic Ga3Ni2 phase.Magnetic and transport results showed that all MnNiGa film samples exhibited anomalies at T=200K,and these anomalies were largely unaffected by deposition temperature or deposition thickness.Due to the presence of the skyrmion topological spin structure in hexagonal Mn NiGa,the material occurred spin-reorientation at 200K,resulting in anomalous phenomena in magnetic and transport properties.The hexagonal pure Mn NiGa films with different Mn contents were prepared by magnetic double target co-sputtering technique,and the structures,magnetic properties and transport properties were measured.A large topological Hall effect was observed in hexagonal MnNiGa films with different Mn contents,and it existed in a wide range of temperature from 10K to 300K.The maximum value reached 143nΩcm at T=250K.Furthermore,we found that the size and the sign of the topological Hall resistance can be manipulated by adjusting the content of the Mn element,and it also showed again that there existed skyrmion in the hexagonal MnNiGa.